two erl.exe processes start when rabbitmq.conf is present

[John McGonigal]

Hi all, hope somebody can help me with this weird issue. I am running RabbitMQ 3.8.2 and Erlang 22.1 on Windows Server 2019.

There is currently no rabbitmq.conf file and I would like to add one, so I stop the service, remove the service, then add a basic rabbitmq.conf file in the correct folder. The rabbitmq.conf file looks like this:

loopback_users.guest = false

I then (re)install and start the service. As the service starts up, an erl.exe process starts, and then a second or so later, another erl.exe process starts, and begins consuming all available CPU. It also eats RAM at about 10Mb/sec. The server becomes almost unusable.

Trying to stop the service via the rabbitmq-service.bat doesn't do anything, but I am able to stop it via the Windows Services GUI. It eventually stops, but leaves behind the 2nd erl.exe process which has to be killed manually.

Whilst it was running, RabbitMQ generates no log file entries.

If I then remove the service, delete rabbitmq.conf, then (re)install the service (it warns that only an advanced.config is present), and start it again, it comes up just fine.

I've tried completely uninstalling RabbitMQ (and removing the RabbitMQ folder) and Erlang and rebooting and then re-installing everything (several times), and it is always exactly the same.

We have other RabbitMQ setups with the same configuration and they work ok, so there must be something different with this one but I'm afraid I am at a loss as to what it might be.

Just wondered if anybody had any ideas or could point me in a direction that would allow me to get to the bottom of it. 

Many thanks in advance,

John

[Luke Bakken]

Hi John,

My guess is that this server only has one physical or virtual CPU available to it. Is that the case?

This is a known bug in the Erlang VM. If you increase the CPU count to 2 or more, it will be resolved.

Thanks,

Luke

[Michael Klishin]

And the bug was supposedly addressed in Erlang 23, which RabbitMQ 3.8.4 supports with minimal limitations (see release notes on https://rabbitmq.com/changelog.html).

But we haven’t tried this single core VM experiment on Erlang 23, only filed a bug with the Erlang/OTP team

and watched it be addressed and closed.

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[John McGonigal]

Thank you Luke and Michael for your quick replies. You were spot on - this was a test server that had been setup with just one CPU. That has now been changed and everything is working fine.

Thanks again,

Best regards,

John

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[Michael Klishin]

Thank you for confirming, John.

 

If I may ask for a favor: would you mind trying to reproduce this on a single core VM with Erlang 23 and see if the issue is actually gone

as we believe it should? That would greatly help us with documenting this behavior and the recommended workaround(s).

 

Thank you.

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[John McGonigal]

Hi Michael, of course no problem. I am away from the office this week but will try this next week and get back to you as soon as I can.

John

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[John McGonigal]

Hi Michael,

Yesterday I tried Erlang 23 and RabbitMQ 3.8.4 on my test VM. I reduced the number of processors back down to 1, and tried starting RabbitMQ firstly without a rabbitmq.conf file. I then re-installed the service with a simple rabbitmq.conf file present. Both times it started up within a few seconds and CPU usage spiked only briefly before settling back down to almost nothing, as it usually does.

I then put the processors up to 4 and repeated the test (with and without a rabbitmq.conf file), and it was about the same.

So it looks like that problem is resolved.

Hope that helps - let me know if you want me to test anything else.

Cheers,

John

[Luke Bakken]

Hi John,

We really appreciate you taking the time to test this and following up here. Glad to see the issue appears to be resolved.

Thanks,

Luke